The neurochemical, behavioral and drug-structural mechanisms through which fenfluramine congeners such as amphetamine act to produce human drug abuse, are unclear. The proposed research effort will evaluate the extent to which various drugs can selectively antagonize the locomotor-stimulant, stereotypy-inducing, reinforcing and operant rate-dependency effects of amphetamines in mice. The effects of such drug interactions on brain regional catecholamine disposition (including brain epinephrine) will also be examined both in vitro and in vivo.